Why do some display Modes Give Caca?

In the attached file I have a polysrf that looks fine under some display modes.
Problem Modes.zip (333.3 KB)
If I do pen or technical mode I get stray lines

Why the difference?

dear Miano - your document-Tolerance is 0.01 inch, there are details with 0.04 inches. I think it would be a good decision to have at least Factor 10 or better Factor 100 between document Tolerance and desired minimum detail.

how did you model the object ? i think it is more the “making of” that causes the error.
but maybe it s a bug.

If I _extractSrf a single Surface in question and then _split (isocrv yes, shrink=yes) _rebuild the part that causes the error, the problem is gone.

maybe this helps, kind regards -tom

Problem Modes 2.3dm (3.1 MB) Problem Modes 2.zip (200.6 KB)

The precisions was 0.001 for construction. I guess I copied it to a file with larger precisions.

Here’s how to make it.

Subtract Layer 2 from Layer 1. Add Layer 3. Subtract Layer 4.